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06828c5feb
Allow messages to be sent at different times, and greatly reduce the frequency of hot standby feedback. Refactor to allow additional message types.
95 lines
2.7 KiB
C
95 lines
2.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* walprotocol.h
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* Definitions relevant to the streaming WAL transmission protocol.
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*
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* Portions Copyright (c) 2010-2011, PostgreSQL Global Development Group
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*
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* src/include/replication/walprotocol.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef _WALPROTOCOL_H
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#define _WALPROTOCOL_H
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#include "access/xlogdefs.h"
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#include "utils/timestamp.h"
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/*
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* Header for a WAL data message (message type 'w'). This is wrapped within
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* a CopyData message at the FE/BE protocol level.
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*
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* The header is followed by actual WAL data. Note that the data length is
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* not specified in the header --- it's just whatever remains in the message.
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*
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* walEnd and sendTime are not essential data, but are provided in case
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* the receiver wants to adjust its behavior depending on how far behind
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* it is.
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*/
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typedef struct
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{
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/* WAL start location of the data included in this message */
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XLogRecPtr dataStart;
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/* Current end of WAL on the sender */
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XLogRecPtr walEnd;
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/* Sender's system clock at the time of transmission */
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TimestampTz sendTime;
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} WalDataMessageHeader;
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/*
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* Reply message from standby (message type 'r'). This is wrapped within
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* a CopyData message at the FE/BE protocol level.
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*
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* Note that the data length is not specified here.
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*/
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typedef struct
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{
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/*
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* The xlog locations that have been written, flushed, and applied
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* by standby-side. These may be invalid if the standby-side is unable
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* to or chooses not to report these.
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*/
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XLogRecPtr write;
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XLogRecPtr flush;
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XLogRecPtr apply;
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/* Sender's system clock at the time of transmission */
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TimestampTz sendTime;
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} StandbyReplyMessage;
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/*
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* Hot Standby feedback from standby (message type 'h'). This is wrapped within
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* a CopyData message at the FE/BE protocol level.
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*
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* Note that the data length is not specified here.
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*/
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typedef struct
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{
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/*
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* The current xmin and epoch from the standby, for Hot Standby feedback.
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* This may be invalid if the standby-side does not support feedback,
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* or Hot Standby is not yet available.
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*/
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TransactionId xmin;
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uint32 epoch;
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/* Sender's system clock at the time of transmission */
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TimestampTz sendTime;
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} StandbyHSFeedbackMessage;
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/*
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* Maximum data payload in a WAL data message. Must be >= XLOG_BLCKSZ.
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*
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* We don't have a good idea of what a good value would be; there's some
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* overhead per message in both walsender and walreceiver, but on the other
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* hand sending large batches makes walsender less responsive to signals
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* because signals are checked only between messages. 128kB (with
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* default 8k blocks) seems like a reasonable guess for now.
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*/
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#define MAX_SEND_SIZE (XLOG_BLCKSZ * 16)
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#endif /* _WALPROTOCOL_H */
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